A 96-year-old man with a rapidly growing right chest wall mass was referred to our department for further treatment. Enhanced chest computed tomography showed a huge pectoral hematoma (12×6 cm) in the right thorax. He was on oral antiplatelet medication, but no abnormalities in clotting ability were detected. Because the hematoma was enlarging and painful, it was evacuated surgically and hemostasis achieved around the pectoral branches of the thoraco-acromial artery. His postoperative course was uneventful with no evidence of subcutaneous fluid retention. Surgical hemostasis and hematoma evacuation of this pectoral hematoma might be effective as one treatment method